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Heavy Water as a Probe of the Free Radical Nature and Electrical Conductivity of Melanin

Shermiyah B. Rienecker, A. Bernardus Mostert, Gerhard Schenk, Graeme R. Hanson, Paul Meredith Orcid Logo, Bernard Mostert Orcid Logo

The Journal of Physical Chemistry B, Volume: 119, Issue: 48, Pages: 14994 - 15000

Swansea University Authors: Paul Meredith Orcid Logo, Bernard Mostert Orcid Logo

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Abstract

Melanins are pigmentary macromolecules found in many locations throughout nature including plants and vertebrate animals. It was recently proposed that the predominant brown-black pigment eumelanin is a mixed ionic–electronic conductor which has led to renewed interest in its basic properties as a m...

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Published in: The Journal of Physical Chemistry B
ISSN: 1520-6106 1520-5207
Published: 2015
Online Access: Check full text

URI: https://cronfa.swan.ac.uk/Record/cronfa38482
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Abstract: Melanins are pigmentary macromolecules found in many locations throughout nature including plants and vertebrate animals. It was recently proposed that the predominant brown-black pigment eumelanin is a mixed ionic–electronic conductor which has led to renewed interest in its basic properties as a model bioelectronic material. This exotic hybrid electrical behavior is strongly dependent upon hydration and is closely related to the free radical content of melanin which is believed to be a mixed population of two species: the semiquinone (SQ) and a carbon-centered radical (CCR). The predominant charge carrier is the proton that is released during the formation of the SQ radical and controlled by a comproportionation equilibrium reaction. In this paper we present a combined solid-state electron paramagnetic resonance (EPR), adsorption, and hydrated conductivity study using D2O as a probe. We make specific predictions as to how the heavy isotope effect, in contrast to H2O, should perturb the comproportionation equilibrium and the related outcome as far as the electrical conductivity is concerned. Our EPR results confirm the proposed two-spin mechanism and clearly demonstrate the power of combining macroscopic measurements with observations from mesoscopic probes for the study of bioelectronic materials.
Item Description: This article has been internally assed for REF, 3 star.
Keywords: melanin, free radical, electron paramagnetic resonance, heavy water, semiquinone, carbon centered radical
College: College of Science
Issue: 48
Start Page: 14994
End Page: 15000